(1) Field of the Invention
The present invention relates to correlation of sonar images and more specifically to finding peaks in correlation images to co-register sonar images using a threshold based on a statistical model and a desired probability of false detections.
(2) Description of the Prior Art
As is known in the art, there are many applications for which it is necessary to determine the relationship between two images. As an example, forming enhanced apertures according to the open/closed aperture theorem, such as combining grid lines to create “circular Synthetic Aperture Sonar (SAS)” like images, requires one to co-register images created during different survey legs or by different robots.
Also, when navigating using a Kalman filter, the relationship between two images can be compared to a predicted relationship, and the difference can be used to improve the state estimate. In addition, when mosaicking, the relationship between images can be used to stitch images together and generate a single, larger image. Still further, when searching for targets, it is desirable to know that there are targets in an image, and to know where they are.
When correlating two sonar images it is often necessary to determine whether or not the images are of the same object or terrain, and the relative position and orientation of one image with respect to the other. This can require choosing a peak in the correlation image and determining whether its value is significant. For navigational algorithms, it is often desirable to use a detection criterion with a low false alarm rate.
However, the correlation coefficients in a correlation image are difficult to predict as they depend on the amount of structure being imaged, the background noise in the environment, and the degree of frequency and aspect overlap. What are needed are systems and methods for detecting correlation in images.